[cmelbye]

This isn't correct. If you've ever resized an application window in OS X, it's likely that you've used autolayout. iOS has the same functionality. In addition to a flexible layout system, iOS has the concept of size classes which determine appropriate content to show based on display size.

[icoder]

But I can imagine that many iOS apps still use 'a fixed layout', as the parent comment stated (or perhaps at max use the old struts and springs mechanism). This may be quite a few and they could all break if Apple had not come up with the 'cheat', as the top comment called it.

[cmelbye]

I still don't understand the "cheat". Any well-designed app that wants to take advantage of larger screen sizes on the new iPhones to display more content will use autolayout and the new size classes (compact and regular). There is no cheating involved.

For transition purposes, apps that haven't been updated yet will simply be scaled up (everything on screen will be slightly bigger). This is similar to when the iPhone 5 introduced a lengthened screen and apps were letterboxed until they submitted an update confirming that they were compatible with the larger screen.

[prof_hobart]

I doubt that too many do, or at least many that are actively maintained.

The introduction of the taller iPhone 5 screen, and Apple's subsequent rejection of "letterboxed" apps (ones that don't make any use of the additional screen space) mean that most developers will almost certainly have switched to autolayout.